1. Field of the Invention
The present invention relates to a highly stable aqueous resin composition comprising a water soluble magnesium salt and an aqueous polyurethane, as well as a recording material, an ink jet recording material, and an ink jet recording method using the same. Specifically, the present invention relates to an aqueous resin composition, a recording material, an ink jet recording material and an ink jet recording method useful for applications to paints, inks, coatings and adhesives, wherein by incorporating a water soluble magnesium salt, the long term stability and the film formation improves.
2. Description of the Background Art
Aqueous polyurethanes with a hydrophilic group within the molecule generally do not require the use of an emulsifier, and consequently films formed therefrom display excellent water resistance, making them ideal for applications such as the various types of paint, inks, coatings, adhesives and recording materials.
However, aqueous polyurethanes produced using a strongly hydrophobic polyester polyol or polycarbonate polyol as a raw material display a rapid evaporation rate for the solvent medium, particularly water, and as a result have suffered from stability problems such as skin formation during storage. Furthermore, when applied to a substrate of any of the potential applications, because the evaporation rate of water from the film is rapid, problems can arise during the film formation such as a non-uniform film thickness or even the appearance of cracks.
A method for improving these problem areas by adding a high boiling point solvent to the aqueous polyurethane is known, but the resulting odors and related environmental concerns mean that this method is not entirely satisfactory, and in certain applications the method is completely unusable.
In addition, conventional applications of aqueous polyurethanes to water based paints, adhesives, inks, and recording materials are known to suffer from a variety of problems.
For example, when used as a water based paint, the non-uniformity of the paint film reduces the functionality of the film including the weather resistance, the water resistance and the chemical resistance, and the exterior surface of the paint film is also susceptible to problems. In addition, the adhesion of the paint to a substrate and the recoatability also deteriorate significantly.
In the field of adhesives, the adhesive strength is largely dependent on the adhesive layer, and in particular on the uniformity of the adhesive film thickness, and so the problems described above are critical.
When used in an ink, because the ink is more susceptible to skinning, for example inside the ink filled vat of a Gravure printer, trouble is more likely to occur during continuous print runs. In addition, the ink can also cause printing failure such as plate jamming.
In the field of recording materials, recording materials comprising a polyurethane resin or another resin composition applied to a substrate such as a synthetic resin film or a piece of paper, for use with ink jet printers, thermal transfer printers, laser printers or offset printers are already known. As the aforementioned resin composition, an aqueous polyurethane displays excellent performance in any printing application regardless of the printing method employed, and Japanese Unexamined Patent Application, First Publication No. Hei 10-181189 discloses an aqueous polyurethane composition combined with a water soluble epoxy compound, an acetoacetylated polyvinyl alcohol, or an epichlorohydrin polyamide resin.
However, even a recording material using this composition does not display ideal film uniformity and ink absorption, and particularly in the case of printing with an ink jet printer using pigment inks, finely detailed printed images are unattainable.
Furthermore recently in the field of recording materials, printers which utilize inks containing dye are used for printing, but the quality is unsatisfactory for use as a recording material for illuminated advertising. In other words, in illuminated advertising the printed surface of the recording material is often laminated with a light fast film to enable use outdoors, which means the recording material must have good durability, good water resistance, and also be suitable for lamination, but recording materials which utilize inks containing dye are not entirely satisfactory in any of these respects.
Accordingly, pigment inks are now being used as the printer inks in the rapidly expanding field of illuminated applications. However, in terms of the resin composition used as the ink receiving layer of the recording material, no resin existed which was able to adequately satisfy the requirements of binder dispersibility, strength of the product recording material, and smoothness of the applied film surface.